Ancient plants mark climate blip

FOSSIL plants are providing an ingenious way of "breathalysing" the Earth's prehistoric atmosphere. By counting the number of pores, or stomata, in fossilised leaves, an Irish palaeobotanist says that she can work out detailed fluctuations in atmospheric concentrations of carbon dioxide over the past 400 million years. The new method has already revealed a CO2 surge in the Eocene period, some 50 million years ago.

Plants open and close their stomata to regulate the amount of CO2 they take up and the amount of water they lose through evaporation. And if they live for a long time in an atmosphere rich in CO2, they will grow leaves with fewer pores. When she was working at Trinity College, Dublin, Jenny McElwain compared recent fossils with related, living species, and found that prehistoric plants had responded in the same way.

Now working at Royal Holloway College, London, with a colleague, Bill Chaloner, ...

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